1. Field of the Invention
The present invention relates to the testing of terminals, and more particularly to a method and an apparatus to monitor, over a period of time, the integrity of terminals inside a semiconductor package assembly.
2. Description of the Prior Art
The reliability of semiconductor products have been tested by operating the semiconductor products in various environments over prolonged periods of time, until they fail and then, inspecting the device to determine the cause of failure. In order to reduce the time to failure, it is common practice to operate the devices being tested under stress, i.e. at elevated temperatures that are well above the normal operating temperatures, under adverse environmental conditions, such as corrosive environments, thermal cycling, etc. These measures are calculated to increase the stress and thereby cause failure at some proportional length of time, relative to operation at normal conditions. Failure of Aluminum (Al) stripes on semiconductor devices due to electromigration has been extensively studied by increasing the current density in the stripe, and the temperature of operation, to produce failure in greatly reduced times than could be obtained by normal operation. This type of testing is described by Hisao Katto in an article entitle, "Wafer Level Joule-heated J-Constant EM Tests", in 1992 WRL Final Report, Pages 176-197.
An article describing the monitoring of moisture in a hermetic package by Lowry et al, entitled, "Characteristics Of A Surface Conductivity Moisture Monitor For Hermetic Integrated Circuit Packages", appears in CH 1425 8//79/0000-0097 $ 00.75 c 1979 IEEE, Pages 97-100. Another article by J. S. Sweet, entitled "The Use Of Special Purpose Assembly Test Chips for Evaluating Reliability In Packaged Devices", published by Sandia National Labs, Pages 15-19. It describes a series of special purpose assembly test chips to aid in reliability assessment of packaged integrated circuits. These chips contain special purpose circuits or sensors which either enhance the detection of failures, or the detection of moisture, or containments, which can lead to device failure.